Skeleton structure members made by filling a skeleton member with a granular bulk material are known from for example JP-A-2002-193649, U.S. Pat. No. 4,610,836 and U.S. Pat. No. 4,695,343. Also, skeleton structure members made by filling a skeleton member with a gel are known from for example JP-A-9-136681.
FIG. 13 shows a solidified granular bulk material of a skeleton structure member disclosed in JP-A-2002-193649.
As shown in FIG. 13, the solidified granular bulk material 200 is made up of multiple granules 201 and a binder 202 consisting of a resin or an adhesive packed between the granules 201 to solidify the granules 201, whereby the granules 201 are bonded together into a solid. The granules 201 are packed into a mold in a dense state, and then the binder 202 is poured in to form the solidified granular bulk material 200. This solidified granular bulk material 200 is inserted into a skeleton member of a vehicle body or the like to make a skeleton structure member, and the strength and rigidity of the vehicle body is thereby raised.
FIG. 14 shows a solidified granular bulk material of a skeleton structure member set forth in U.S. Pat. No. 4,610,836 and U.S. Pat. No. 4,695,343.
This solidified granular bulk material 210 made by bonding together and thereby solidifying multiple granules for insertion into a skeleton member is made up of multiple small glass spheres 212 serving as granules coated with an adhesive 211. These glass spheres 212 are wrapped with a cloth made of glass fiber and packed into a skeleton member to make a skeleton structure member.
FIG. 15 shows a skeleton structure member disclosed in JP-A-9-136681. This skeleton structure member 220 has a gel 223 packed between two lower panels 221, 222. The reference number 224 denotes an orifice provided in the lower panel 222, and 225 a cap for plugging the orifice 224.
For example when in a vehicle collision or the like an excessive pressure arises in the gel 223, the cap 225 comes out under that pressure and allows the gel 223 to spurt out, whereby impact energy is absorbed.
A crush test method for applying a load to and forcibly breaking a skeleton structure member and results of crush tests carried out by this method on the skeleton structure members of related art shown in FIG. 13 to FIG. 15 are shown below.
FIG. 16 and FIG. 17 show details of the crush tests carried out on the skeleton structure members of related art, FIG. 16 illustrating the crushing and FIG. 17 being a graph showing the results of the crush tests.
In FIG. 16A, a skeleton structure member 232 made by filling a skeleton member 231 having a hollow square cross-section with granules is forcibly deformed by a compressive load F being applied to it in the length direction as shown with an arrow.
In FIG. 16B, when the deformation of the skeleton structure member 232, and specifically the displacement of the end of the skeleton structure member 232 under the load, is written λ, as the displacement λ increases the skeleton structure member 232 either buckles into a bellows shape or bends into a Z shape like that shown in the figure or into a dog-leg shape.
FIG. 17 is a graph showing the relationship between the load F and the displacement λ of the skeleton structure member when it is deformed as shown in FIG. 16B. The vertical axis shows the load F and the horizontal axis the displacement λ. Four test pieces were used: Comparison Example 1 (unfilled), which was a skeleton member only, not packed with any filler; Comparison Example 2 (granules bonded with binder), which was that shown in FIG. 13 made by bonding granules with a binder; Comparison Example 3 (small spheres bonded with adhesive), which was that shown in FIG. 14 made by bonding small spheres with an adhesive; and Comparison Example 4 (low-strength granules) filled with a granules of lower strength than Comparison Example 2 and Comparison Example 3.
In Comparison Example 1, the load F is small but the displacement λ at which the skeleton member collapses into a bellows shape is large. The displacement d1 at this time is the displacement at which the skeleton member collapses completely, and is the effective stroke (that is, the displacement λ from zero to d1) over which energy applied from outside can be absorbed effectively. After this effective stroke the load F increases sharply.
Comparison Example 2 to Comparison Example 4 are shown as far as their effective strokes.
The area in the effective stroke region sandwiched between the line of Comparison Example 1 and the horizontal axis shows the energy absorbed by the skeleton structure member of Comparison Example 1, and the value obtained by dividing this absorbed energy by the effective stroke is the load f1 in the figure. That is, this load f1 is the average load in of Example 1.
From this, to increase the energy absorbed by a skeleton structure member, a high average load and a long effective stroke are necessary.
In Comparison Example 2 (granules bonded with a binder, described with reference to FIG. 13), the average load is very large but the displacement λ is not so large. This is because, since the bonding of the granules is extremely strong, in the initial stage of deformation the internal pressure of the skeleton member rises excessively and the member bends into a Z-shape or a dog-leg shape, and after that the load decreases sharply. Consequently, the absorbed energy is not that much greater than that of Comparison Example 1.
In Comparison Example 3 (small spheres bonded with adhesive, described with reference to FIG. 14), for the same reason as in Comparison Example 2, the average load is large but the displacement λ is not that large, and the absorbed energy is not much greater than that of Comparison Example 1.
In Comparison Example 4 (low-strength granules), because the granules themselves break up easily and the rise in the internal pressure of the skeleton structure member is not that sharp and the member does not bend into a Z-shape or a dog-leg shape, although the displacement λ is greater than in Comparison Example 2 and Comparison Example 3, because the granules remain inside the skeleton structure member, the displacement λ is smaller than in Comparison Example 1. Also, the average load is small, and as a result the absorbed energy is small.
From the foregoing results, it can be seen that it is difficult to raise the average load of a skeleton structure member and simultaneously extend its effective stroke.
With the skeleton structure member 220 shown in FIG. 15, because it is filled with the gel 223, when a load acts on the skeleton structure member 220, the gel 223 flows smoothly and spurts out through the orifice, and consequently the internal pressure of the skeleton structure member 220 is kept roughly constant during the deformation. As a result, local deformation does not arise, and a relatively large load can be maintained up to a large displacement.
However, when the skeleton structure member is filled with granules, because due to frictional forces between the granules the fluid motion of the granules is not as smooth as the fluid motion of the gel 223, it is difficult to keep the internal pressure constant.
This will now be explained in detail with reference to FIG. 18 to FIG. 20.
FIG. 18 shows deformation of a skeleton structure member having one drain hole for granules to discharge through like the skeleton structure member 220 shown in FIG. 15.
As shown in FIG. 18A, this skeleton structure member 240 is made up of a skeleton member 241, multiple granules 242 packed inside this skeleton member 241, and a cap 244 plugging a drain hole 243 formed in the skeleton member 241 to allow the egress of these granules 242.
As shown in FIG. 18B, a compressive load F is applied to the skeleton structure member 240 in its length direction as shown with an arrow. As a result, the internal pressure of the skeleton member 241 increases sharply, and the granules 242 push out the cap 244 shown in FIG. 18A and spurt out to outside through the drain hole 243.
As illustrated in FIG. 18C, the internal pressure of the granules 242 in the vicinity where the granules 242 have spurted out falls, the strength of the part near the drain hole 243 of the skeleton structure member 240 decreases, and the whole member bends about this part. As a result, the load supported by the skeleton structure member 240 becomes very small. Consequently, the energy absorbed by the skeleton structure member 240 is small.
FIG. 19 shows deformation of a skeleton structure member having a plurality of drain holes like that shown in FIG. 18.
The skeleton structure member 250 shown in FIG. 19A is made up of a skeleton member 251, multiple granules 242 packed into this skeleton member 251, and caps 254, 256 plugging a plurality of drain holes 252, 253 formed in the skeleton member 251 to allow the granules 242 to flow out.
As shown in FIG. 19B, a compressive load F is applied to the skeleton structure member 250 in its length direction as shown with an arrow. As a result, the internal pressure of the top of the skeleton member 251 increases sharply and the granules 242 push out the upper cap 254 shown in FIG. 19A and spurt out to outside through the drain hole 252.
As shown in FIG. 19C, the internal pressure of the granules 242 in the vicinity where the granules 242 spurted out falls, the strength of the part of the skeleton structure member 250 near the drain hole 252 decreases, and the whole member bends about this part.
When the load F is increased further, the internal pressure of the bottom of the skeleton structure member 251 increases and the granules 242 push out the lower cap 256 shown in FIG. 19B and spurt out to outside through the drain hole 253, and consequently the skeleton structure member 250 bends about the part around the drain hole 253 as shown in FIG. 19D.
Because bending occurs at the part near the drain hole 253 and the whole member folds like this, the load fluctuates markedly and as a result the absorbed energy does not increase.
FIG. 20 is a graph showing crush test results of the skeleton structure members 240, 250 shown in FIG. 18 and FIG. 19.
In the case of Comparison Example 5 (the skeleton structure member 240), which has one drain hole, the load F is small and the maximum value of the displacement λ is also small, and consequently the absorbed energy is low.
In the case of Comparison Example 6 (the skeleton structure member 250), which has a drain hole in each of a plurality of locations, the member displaced to a relatively large displacement d2 with the load F fluctuating greatly.
The numeral f2 in the graph is the average load of Comparison Example 6, and because this is not that large, the absorbed energy is also not that great as a result.
Accordingly, technology for increasing the energy absorbed by a skeleton structure member for use in a transport machine has been awaited.